So when the posession is surendered after the four failed attempts at getting downs and the teams role reverses from offence to defence and vice versa so they then go and change all of their players over?

There are two different kinds - 'red' and 'celebrity' - which one you are depends whether or not you went to an Ivy League college.

And for your own sake, rid yourself of the concepts of rucks and lineouts - like rugby league you don't compete for the ball, it's either your posession or it's not (the only exception being if the man carrying the ball drops it - that's a fumble and then it's a free-for-all)

And the ball only ever comes back into play from a snap or a kickoff - never from the sideline.

If the ball or the carrier goes out of bounds, the play restarts from the middle, in line with where they went out.

The most frequent decision made will be how far the ball went, and whether it made the requisite distance (ten yards from the first play or 'down') to reset the play count - so from first play you are "first [down] and ten [yards to go]" - say you run six yards and get tackled, you are then "second and four".

You get four plays to go ten yards - so like in rugby league when they kick it away on the sixth phase, they'll usually punt it away to maximise the distance they have to defend coming back (or go for a field goal if they're close enough).

You can go minus yards - so if on the first attempt ("first and ten" you snap it ten yards back to the quarterback and he gets tackled ("sacked") then you are "second and twenty".

Quarterpounder - As discussed, takes the snap and then distributes the ball in an attempt to gain yards/score.

Wide Receivers - Their job is to catch the passes. You'll usually see them sprinting up the wing like bastards trying to get ahead of some fatso to catch a long-bomb. Surprisingly good at it some of them, considering they're running with their back to the pass.

Running Back - Weasly chap who takes the ball short from the quarterback and tries to run through the line and make ground. Usually employed on the later plays when there are fewer yards to make.

The above three positions score almost all the points between them and hence tend to be the superstars.

The rest of them are assorted linebackers, defensive ends, backscratchers and childfondlers whose job it is to facilitate or disrupt the offensive players and no one really gives a fuck about but do make a good crunching sound at the beginning of the play.